It is important to know that we only use this expression informally.

重要的是要知道，我们只在非正式场合使用这个短语。

Yes, you can use it informally; yes, you can use it in person.

是的，你可以在非正式的场合用它；是的，你可以在面对面交谈的时候用它。

But this idiom is about learning something new by talking to people informally.

但是这个习语是指通过非正式的交谈来了解新的消息。

The act of swimming naked is informally called skinny dipping.

裸着游泳这种行为被通俗地称为裸泳。

OK, but what if you want to greet someone informally?

好了，但是如果你想非正式地问候别人该怎么做呢？

At the moment I work from home so I tend to dress fairly informally.

目前我在家工作，因此我倾向于穿得比较随意。

This is common if you're answering the phone informally and you don't know who's calling.

这是非常常见的，如果在非正式的情形中接电话，并且你不知道谁打来的话。

Of course, speaking informally goes beyond word choice.

当然，非正式语言不仅限于词语选择。

Other translators chose to have Hagrid simply speak more informally, while others dropped his accent entirely.

其他语言的译者选择让海格用较轻浮的方式说话，虽然这样就完全捨弃掉口音。

You think I look too scruffy, and that I made a mistake by dressing too informally.

你认为我看起来太邋遢了，我搞错了场合，穿着太不正式。